This invention relates to a method for manufacturing a magnetic head which is suitable for high density recording.
In conventional ferrite heads, to cope with an increase in the coerciveness of the magnetic recording medium so as to enhance the recording density to increase the of playing time video tape recorder or the like, it is difficult to magnetize sufficiently to a back surface of a magnetic layer. Accordingly, a new magnetic head is developed by disposing a high-magnetization magnetic alloy such as amorphous magnetic alloy, at least in the vicinity of a magnetic gap. An example of a maunfacturing method of such a ring-shaped magnetic head is explained referring to FIGS. 1A; 1B. A plurality of nonmagnetic substrates 22 having a magnetic alloy 23 formed on one side are laminated by way of an adhesive glass 21, and this block is cut in rectangular strips, and a winding window 24 and a glass sump groove 25 are formed on the gap surface, and a nonmagnetic gap film is formed, and by fusing the low melting point glass 27 in sump groove 25 and winding window 24, gapped bars 29, 29' joining two core halves are composed. Sequentially, the gapped bars are cut into a specified core width to obtain head chips 28, and by polishing the tape sliding surface, a magnetic head as shown in FIG. 1B is obtained. Incidentially, in the case of an amorphous magnetic alloy formed by sputtering or similar method, it is necessary to anneal at a high temperature in order to obtain favorable magnetic characteristics. In the case of an amorphous magnetic alloy of which crystallization temperature Tx is higher than the curie temperature Tc, magnetization vanishes at a temperature over Tc. Therefore, when the temperature of the glass bonding during the head fabrication process is selected somewhere between Tc and Tx, the same effect of annealing is obtained at the same time without actually annealing. Generally, however, since the Tx is lower than the Tc in the high-magnetization amorphous magnetic alloy, if a temperature lower than Tx is selected, it is less than Tc, and magnetization exists at the annealing temperature, and it is necessary to anneal while applying a rotary magnetic field or stationary magnetic field in order to avoid unnecessary magnetic anisotropy. This application of magnetic field is needed in the majority of the head manufacturing processes.
Annealing in the magnetic field does not matter in the case of amorphous magnetic alloy on a large rectangular substrate after sputtering, but in the case of a gapped bar with winding groove processing, since the demagnetizing factor differs depending on the shape of the object to be annealed, unnecessary magnetic anisotropy may be left over if the intensity of the applied magnetic field is insufficient. Yet, even when the intensity of the applied magnetic field is sufficiently large, if the demagnetizing factor differs depending on the direction of the magnetic field, the rotation of the magnetization of the magnetic alloy when placed in the rotary magnetic field is not uniform, and a magnetic anisotropy may be left over. FIG. 2 shows the mode of magnetization at point A in a magnetic core near the magnetic gap when a rotary magnetic field is applied in the film surface of the head with a film thickness of 40 .mu.m. In spite of isotropic application of the magnetic field, the direction of magnetization is inclined in the direction of the smaller demagnetizing factor. Especially in the vicinity of the winding window, an anisotropy tends to be formed in the direction along the shape of the window due to the effect of the magnetic charge generated at the end surface of the window. Therefore, when a magnetic head of such shape is annealed in a rotary magnetic field, the magnetic core in the vicinity of the magnetic gap at the winding window side may come to have a magnetic anisotropy in the direction along the winding window. Meanwhile, when the anisotropy of the magnetic core is defined parallel (FIG. 3A) or perpendicular (FIG. 3B) to the magnetic gap face as shown in FIG. 3, leakage of the magnetic flux in the magnetic gap is smaller in the head having a parallel anisotropy to the magnetic gap, but in the head annealed in rotary magnetic field as mentioned above, the anisotropy of the magnetic core in the vicinity of the gap surface is closer to the direction perpendicular to the magnetic gap surface, and it is expected that favorable characteristic may not be obtained. In order to obtain a further preferable high frequency characteristic, when a uniaxial anisotropy is applied by annealing in a stationary magnetic field, similar problems may occur due to the difference in the demagnetizing factor depending on the direction of applied magnetic field.